Invalid virtualenv situation when changing python executable

[avivace]

I'm reporting something that break my envirornment while following the first training sessions.

Basically, in session 3 when you first run the commands to bring up the full docker-compose set up, it asks you to generate a pipfile. If you change your Python executable after having generated this pipfile lock (in my case, 3.8 -> 3.6 happened while trying to fix some other issues that popped out later) this generates a broken situation.

Maybe looking for the pipfile lock and running pipenv lock at the start of build-images.sh can avoid this kind of situations